Blue amphiboles in metamorphosed Mesozoic mafic rocks from the Central Alps

1986 ◽  
pp. 239-248 ◽  
Author(s):  
R. Oberhänsli
Keyword(s):  
Central Alps ◽  
Mafic Rocks

Timing of HP/HT alpine metamorphism: new data from Cima di Gagnone (Central Alps)

2020 ◽  
Author(s):  
Stefania Corvò ◽  
Matteo Maino ◽  
Antonio Langone ◽  
Filippo Luca Schenker ◽  
Silvio Seno ◽  
...  
Keyword(s):  
High Pressure ◽  
Structural Control ◽  
Mafic Rock ◽  
Planetary Science ◽  
Swiss Alps ◽  
Central Alps ◽  
Sample Collection ◽  
Shrimp Dating ◽  
Mafic Rocks ◽  
Ultra High Pressure

<p>Keywords: HP-HT metamorphism, microstructures, U-Pb-Th dating, P-T-t-d path.</p><p>The occurrence of (ultra)high pressure and high temperature mineralogical assemblages developed during the Alpine phases makes the Cima di Gagnone area (Cima Lunga unit) one of the most studied area in the Central Alps. It consists of continental basement rocks (orthogneisses, paragneisses and metapelites) enveloping (ultra-) mafic bodies of oceanic crust (eclogite, amphibolites and peridotites) which record pressure and temperature up to 3 GPa and 800 °C, respectively (e.g. Nimis and Trommsdorff, 2001; Scambelluri et al., 2015). This high-grade metamorphism is constrained between 40 and 35 Ma by U-Pb dating from the ultra-mafic and mafic rocks (e.g. Gebauer, 1999). The metamorphism peak of the surrounding gneiss complex is instead constrained at considerably lower conditions (up to 0.8 GPa and 660 °C; Grond et al., 1995). The temperature peak in the felsic rocks is dated at ca. 32 Ma (Gebauer, 1996), coeval with the Bergell emplacement. Several models have been proposed to explain the coupling between ultrahigh- and middle- pressure rock pairs resulting in a large uncertainty in the adopted subduction-exhumation models.</p><p>We performed new petrological, micro-structural and geochronological data from the gneissic rocks, with the aim to investigate how the pressure and temperature conditions experienced by the felsic and mafic rocks are truly different. We explored the spatial variation of the metamorphic record through sample collection the structural control of the inclusion-matrix couples. Petrological and microstructural (SEM-EBSD) analyses are performed to define the deformation and metamorphic patterns of samples collected. Our results indicate that some portions of the gneissic matrix preserve relicts of higher pressure and temperature than previously suggested. The high-T conditions are temporally constrained by U-(Th)-Pb dating of monazite and zircon, which provides peak age estimations similar to the mafic rocks. The new data shed a light on heterogeneous metamorphism recorded by different rocks, providing new elements for the discussion on the most fitting geodynamic models.</p><p>REFERENCES</p><p>- Gebauer, 1996. A P-T-t Path for an (Ultra?-) High-Pressure Ultramafic/Mafic Rock-Association and its Felsic Country-Rocks Based on SHRIMP-Dating of Magmatic and Metamorphic Zircon Domains. Example: Alpe Arami (Central Swiss Alps). Earth Processes Reading the Isotopic Code, Geophysical Monograph 95, 307-329, AGU.</p><p>- Gebauer, 1999. Alpine geochronology of the Central Alps and Western Alps: new constraints for a complex geodynamic evolution. Schweiz. Mineral. Petrogr. Mitt., 79, 191-208.</p><p>- Grond, R., Wahl, F. and Pfiffner, M., 1995. Mehrphasige alpine Deformation und Metamorpshe in der nordlichen Cima Lunga-Einheit, Zentralalpen (Scweiz). Schweiz. Mineral. Petrogr. Mitt., 75, 371-386.</p><p>- Nimis, P. & Trommsdorff, V., 2001. Revised thermobarometry of Alpe Arami and other garnet peridotites from the central Alps. J. of Petrology, 42, 103-115.</p><p>- Scambelluri, M., Pettke, T., & Cannaò, E. (2015). Fluid-related inclusions in Alpine high-pressure peridotite reveal trace element recycling during subduction-zone dehydration of serpentinized mantle (Cima di Gagnone, Swiss Alps). Earth and Planetary Science Letters, 429, 45-59.</p>

scholarly journals An Integrated Investigation of Atmospheric Gaseous Elemental Mercury Transport and Dispersion Around a Chlor-Alkali Plant in the Ossola Valley (Italian Central Alps)

Toxics ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 172
Author(s):  
Laura Fantozzi ◽  
Nicoletta Guerrieri ◽  
Giovanni Manca ◽  
Arianna Orrù ◽  
Laura Marziali
Keyword(s):  
Elemental Mercury ◽  
Background Concentration ◽  
Dispersion Pattern ◽  
Central Alps ◽  
Gaseous Elemental Mercury ◽  
Mercury Transport ◽  
Close Proximity ◽  
Potential Impact ◽  
Hg Accumulation

We present the first assessment of atmospheric pollution by mercury (Hg) in an industrialized area located in the Ossola Valley (Italian Central Alps), in close proximity to the Toce River. The study area suffers from a level of Hg contamination due to a Hg cell chlor-alkali plant operating from 1915 to the end of 2017. We measured gaseous elemental Hg (GEM) levels by means of a portable Hg analyzer during car surveys between autumn 2018 and summer 2020. Moreover, we assessed the long-term dispersion pattern of atmospheric Hg by analyzing the total Hg concentration in samples of lichens collected in the Ossola Valley. High values of GEM concentrations (1112 ng m−3) up to three orders of magnitude higher than the typical terrestrial background concentration in the northern hemisphere were measured in the proximity of the chlor-alkali plant. Hg concentrations in lichens ranged from 142 ng g−1 at sampling sites located north of the chlor-alkali plant to 624 ng g−1 in lichens collected south of the chlor-alkali plant. A north-south gradient of Hg accumulation in lichens along the Ossola Valley channel was observed, highlighting that the area located south of the chlor-alkali plant is more exposed to the dispersion of Hg emitted into the atmosphere from the industrial site. Long-term studies on Hg emission and dispersion in the Ossola Valley are needed to better assess potential impact on ecosystems and human health.

scholarly journals Evidence of active magmatic rifting at the Ma’Alalta volcanic field (Afar, Ethiopia)

2021 ◽  
Vol 83 (6) ◽  
Author(s):  
Gianmaria Tortelli ◽  
Anna Gioncada ◽  
Carolina Pagli ◽  
Mauro Rosi ◽  
Laura De Dosso ◽  
...  
Keyword(s):  
Seismic Data ◽  
Volcanic Field ◽  
Lava Flows ◽  
Magmatic Activity ◽  
Magma Storage ◽  
Plumbing System ◽  
Mafic Lava ◽  
Cinder Cones ◽  
Mafic Rocks ◽  
Seismic Networks

AbstractDuring continental rifting, strain and magmatism are believed to localize to narrow magmatic segments, while the rift margin is progressively abandoned. We integrate volcanological, geochemical, petrological and seismic data from the Ma’Alalta volcanic field (MVF) near the western margin of Afar, to show that the MVF is an active magmatic segment. Magmatism in MVF initiated with lava flows and large-volume, caldera-forming ignimbrites from a central edifice. However, the most recent magmatic activity shifted towards mafic lava fields, cinder cones and obsidian-rich silicic domes erupted from vents aligned NNW-SSE, defining a ~ 35-km-long magmatic segment. Along the same area, a NNW-SSE alignment of earthquakes was recorded by two local seismic networks (2005–2009 and 2011–2013). The geochemistry of the mafic rocks is similar to those of nearby axial volcanoes. Inferred magma storage depth from mineral geobarometry shows that a shallow, silicic chamber existed at ~ 5-km depth below the stratovolcano, while a stacked plumbing system with at least three magma storage levels between 9 and 24 km depth fed the recent basalts. We interpret the wide set of observations from the MVF as evidence that the area is an active magmatic segment, showing that localised axial extension can be heavily offset towards the rift margin.

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